According to Above the Law, two men in Seattle are each calling themselves the US Attorney for the Western District of Washington. Neither has been confirmed by the Senate. One is the nominee actually put forward by President Trump; the source does not explain the other man's claim to the office.
The article notes that the situation has produced a Spider-Man meme, referencing the scene in which two identical characters point at each other. The meme appears to reflect the confusion of having two people assert the same title without Senate confirmation.
The standoff is unusual because the US Attorney role typically requires presidential nomination and Senate confirmation. With two claimants and no confirmation, the question of who holds lawful authority to lead federal prosecutions in the district remains unresolved. The source does not say how the dispute might be settled.